Airplane propeller



1940- c. SCHMIDT ET AL 12 2 AIRPLANE PROPELLER Original Filed Sept. 15,1957 IN VENTOR.

AT'TORNEY.

Patented Nov. 19, 1940 UNITED STATES AIRPLANE PROPELLER Leopold C.Schmidt and Walter J. Schmidt, Jersey City, N. J.

Refiled for abandoned application Serial No.

163,516, September 13, 1937.

This application March 18, 1940, Serial No. 324,506

1 Claim.

The present application is a refile of our previous application filedSeptember 13, 1937, Serial No. 163,516 and comprises an improvedairplane propeller having aplurality of blades of different length, thelength of each successive blade being in a definite relation to the onepreceding it.

It is a well known fact that airplane propellers having more than oneblade of equal length are very inefiicient. This is due to the fact thatthe high speed of one propeller blade will create an aerial void whichwill not have time to become equalized before the next propeller bladeenters. The following propeller blade therefore has to operate in thisvoid of wake from the preceding '15 one and it thus works in a partialvacuum or a rarefied air which would be equivalent to operating at avery high altitude. It is well known that no propellers are veryeffective at extremely high altitudes and it, is therefore readily seenthat when the propeller speed exceeds a certain limit the effectivenessof a multiple blade propeller must necessarily be greatly diminished.For this reason it has been variously Suggested to use and try a singleblade and while this is possible and gives higher efliciency it hasseveral serious disadvantages due to the dynamic unbalance created. Itis furthermore well known that due to the higher peripheral speed theabove condition is only prevalent at the outer '30 ends of the propellerblades. The present invention proposes to eliminate all thesedifficulties by making the propeller blades of various lengths. w Theobject of our invention is therefore to provide an airplane propellerhaving a plurality of blades which are of different lengths and wherethe length of each shorter blade is a definite mathematical proportionto the length of the longer blade. A further object of our invention isto provide a propeller having a plurality of blades of unequal lengthwhere each blade is made of a difierent material and where the specificgra'vities of these materials are in a definite mathematical relation tothe length of the blades. Still another object of this invention is toprovide a multi-blade airplane propeller of higher efliciency andcapable of giving increased power at lower speed thus being of smallersize fora given 'power. Other objects and' advantages of the inventionwill be apparent from the following specification and claim.

In the accompanying drawing, forming a part of this specification," andin which like numerals are employed to designate like parts throughout 5the same:

Figure 1 is a front view of an airplane propeller having two blades ofunequal length, and,

Figure 2 illustrates an airplane propeller having three blades ofunequal length.

In the drawing, wherein for the purpose of illustration, is shown apreferred embodiment of our invention, the numeral I ll designates thehub of the propeller which has two blades l2 and I3. ,The blades l2 andI3 are fastened to the hub at I4 and IS. The radius to the tip of thelonger blade is given the dimension RI while the radius to the tip ofthe shorter is given the dimension R2. R3 is the radius to the effectivepart of the shorter blade.

Referring to Figure 2, the illustrated three '15 blade propeller has along blade I 6 a shorter blade I1 and a still shorter blade l8 equallyspaced around the hub ID. The radius to the tip of the-longer blade isRI, the radius to the tip of the next shorter blade I1 is R2, the radius'20 to the tip of the shortest blade is R3 and the radius to theeffective part of the shortest blade I8 is R4. It will be noted that ineach case the radius to the tip of a shorter blade is always equal tothe radius of the eflective part of the 25 next longer one.

The relation between the various blades can be shown mathematically asfollows:

For the purpose of the mathematical treatment the following denotationsare used: 30

R1=length of the longest blade R2=length of the next shorter bladeR3=length of the next shorter blade I1 =moment of inertia of longestblade 35 I2 =moment of inertia of next shorter blade M1 =mass of thelongest blade M2 =mass of the next shorter blade W1=welght of thelongest blade Wz=weight of the next shorter blade Q1 =cross section ofthe longest blade 40 Q2 =cross section of the next shorter blade 'w1=specific gravity of material used in the longest blade wz =specificgravity of material used in the next shorter blade 9 =acceleratio'n ofgravity.

The moment of inertia may be expressed for each blade as follows:

Equation 2 may be further simplified by making Q1=Qz and we have then:

I1/Iz=w1R1 /w2R2 (35 To be dynamically balanced the above ratio of themoments of inertia for a two-bladed propeller must be equal to one. Thespeed is the same forboth blades, hence we may write:

w1R1 =w2R2 (4) From this equation it is possible to find the properlength of each blade for correct dynamic balance when the blades aremade from materials of different specific gravity:

R =RN w /w 5) If for example the two blades of a propeller are made fromDow metal of spec. gr. 1.? and Dural of sp. g. 2.8 we have:

In other words the longest blade must be 18% longer than the shorterone. By using wood or metallic alloys of the desired specific gravitiesdynamically balanced propellers may be produced which have the propergraduations in blade length to give better efilciency for each blade andless noise and vibration. Propellers with three or more blades may becalculated in the same way. In the latter case the components of themoments of inertia of thetwo or more shorter blades must be equal to themoment of inertia of the longest blade. This may be expressed as followsfor a three-blade propeller:

I1=I2.COS 60+13.005 60. hence: I1= /z(1'2+I3).

The ratio for dynamic balance must be one:

I 1 I w Rfi (6) 1 m i U: 3) E t- 2 a 'z Now cos 60=0.5 and From Equation6 the length of the blades of higher efliciency and of higher power atlower speeds thus permitting a smaller over-all size..

The longer blade of the propeller will create a void in the spacebetween R! and R2, the next shorter blade will work inside of the radiusR2 and will thus not be afiected by the wake of the longer blade. thethird blade in a three-blade propeller.

It is to be understood that the form of our invention, herewith shownand described is to be taken as a preferred example of same, and thatvarious changes in the shape, size and arrangement of parts may beresorted to without departing from the spirit of our invention, or thescope of the subjoined claim.

Having thus described our invention we claim:

A propeller of the character described having a plurality of blades ofunequal length, each shorter blade having its length determined inrelation to the length of the next longer blade, by

and each blade being made of a difierent material in such a way thateach shorter blade is made of a heavier material than the next longerone and that the specific gravities of these materials be relatedaccording to the following formula: w1=w2R2=/R1 LEOPOLD C. SCHMIDT.

WALTER J. SCHMIDT.

The same thing happens with

